1. Field of the Invention
The instant invention relates to a valve incorporating a pressure-balanced piston and more particularly to such a valve which may be used as a pressure regulating, pressure relief or pressure reducing valve.
2. Description of the Related Art
Numerous types of pressure reducing, pressure regulating and pressure relief valves are known in the prior art. Some of these valves include a pressure-balanced piston which is slidable in a bore formed in a valve body. Typically, the lower surface of the piston includes a needle or cone which is movable toward and away from an orifice thereby regulating flow therethrough. In operation, fluid flows into the valve beneath the piston and out through the orifice. Typically, the upper surface of the piston is exposed to fluid pressure upsteam or downstream from the valve. A pressure relief valve has an inlet in fluid communication with the upper surface of the piston and thereby prevents the pressure above the piston from rising above a preselected level.
Such prior art valves suffer from several disadvantages. Because of the continuous movement of the piston, o-rings usually are not used to seal about the circumference of the piston due to the high rates of wear which would be encountered. Thus, such pistons are typically machined, sometimes within a tolerance of fifty millionths of an inch (0.000050), to be slidingly and sealingly received in an associated valve body. Such valves are expensive and subject to rapid wear.
Such prior art valves also do not have sufficient speed of response to changes in pressure in some applications, because the relief valve above the piston is not sufficiently responsive to pressure changes. This may be a result of flow restrictions such as tubing, bores or the like which communicate fluid to the inlet of the relief valve and which delay rapid pressure changes from being communicated thereto. In such valves, pressure is not accurately regulated over a wide range of flows and in some such valves is not regulated accurately for any flow rate.